The project aims at measuring the rate constants of reactions of DNA radicals which are intermediates formed by anti-cancer agents such as bleomycin that result in DNA destruction. Kinetic measurements will be accomplished by laser flash photolysis (LFP) methods employing kinetic spectrometers with nanosecond resolution. The radicals will be produced from precursors that are known to be useful in LFP studies. Because DNA radicals can react by a number of pathways, the kinetics of second-order reactions with thiols and first- order phosphate elimination reactions will be measured directly in aqueous solutions, and these kinetic values will serve as the foundation for a DNA radical kinetic scale. C1' radicals from ribose and 2- deoxyribose nucleosides, produced by laser photolysis, will be characterized spectroscopically, and the kinetics of reactions of these species will be measured by direct observation of the rates of decay of the UV absorbances. C4' and C3' radicals of nucleosides and 2- deoxynucleoside and C4' DNA radicals, which do not contain useful chromophores, will be monitored by the use of background reporter reactions that produce UV-detectable transients. Studies of the mechanism of fragmentation of beta-phosphate radicals, including kinetic isotope effect studies, will focus on the generality of a concerted elimination pathway that was recently discovered. Because many clinical therapeutic approaches to cancer treatment involve the use of agents that destroy DNA via radical intermediates, a good understanding of the kinetic and mechanisms of reactions of these species will be important for future drug development.